The present invention relates in general to an image forming apparatus. More particularly, the invention relates to an image forming apparatus of the type which has a developing device that is installed detachably and, thus, is suitable for feeding toner, as well as replacing the toner cartridge or the developing device.
Conventionally, in an image forming apparatus which operates by forming an electrostatic latent image on a photosensitive body, a developing device is provided in order to make the electrostatic latent image visible by applying a toner thereto. The developing device is installed in the image forming apparatus mainly for feeding the toner, and is typically detachably mounted for facilitating replacement or maintenance of the developing device.
When this kind of image forming apparatus is manufactured as an original-equipment manufacturer (OEM) product to be sold under various brands by a plurality of different companies, it is required to provide constructions for the toner cartridge and/or developing device to permit loading only of the image forming apparatus of the corresponding brand (which will be hereinafter referred to as xe2x80x9cproviding non-compatibilityxe2x80x9d for the toner cartridge and/or the developing device).
Conventionally, the external shape of the developing device varies significantly per brand, and the loading portion of the developing device in a main body of the image forming apparatus is designed to make it impossible to load a developing device of a brand other than the specific or designated brand of the image forming apparatus for the purpose of providing non-compatibility with other brands. However, in case of an image forming apparatus to be provided for sale under a plurality of brands, it becomes necessary, if non-compatibility is provided, to manufacture developing devices each having a different shape for each brand, which will inherently result in an increase of the manufacturing cost of the developing device and to make manufacture, storage, handling and so forth of the developing device quite troublesome.
On the other hand, Japanese Patent Application Laid-Open No. 7-134497 (1995) discloses an image forming apparatus provided with a simple electrical signal relay means in order to detect loading of a particular kind of developing device in the main body of the image forming apparatus.
Also, in case of a full color image forming apparatus of this kind, for example, typically four developing devices respectively using toners of yellow, magenta, cyan and black, or three kinds of developing devices respectively using toners of yellow, magenta and cyan are provided. To accommodate these developing devices of different colors, the image forming apparatus is provided with a plurality of developing device loading portions. In many cases, the positions accommodating the respective developing devices of different colors are fixed in the image forming apparatus. In such a case, the developing devices of the respective colors have to be loaded at the correct loading portions. For example, in the case of the yellow developing device, steps need to be taken so that this developing device will not be loaded in the loading portion for a developing device of another color in the image forming apparatus. The same is true for the developing devices of the other colors. Namely, non-compatibility has to be provided for the plurality of developing devices to be loaded in the same image forming apparatus. Even for an image forming apparatus other than one of the full color type, when a plurality of kinds (two or more kinds) of developing devices are used in the image forming apparatus and the respective loading portions of the respective developing devices are fixed, non-compatibility has to be provided for the respective developing devices.
In a former restricting means, by differentiating on the basis of external shape, when a member to be engaged is employed as the restricting means, the restricting means can be rendered ineffective by removing an engaging portion of the engaging member or by removing the engaging member itself. Also, in the case of the arrangement disclosed in Japanese Patent Application Laid-Open No. 7-134497 (1995), detection of loading of the developing device is performed by means of a connector, which is provided at a position where it will not mate with the engaging member, and with use of a simple electric signal relay member. Therefore, when the developing device, from which the engaging portion or the engaging member per se has been removed, is not the correct one to be loaded in the relevant loading portion, it is possible to make an erroneous detection that the correct developing device has been loaded, thereby to permit operation of the developing device under unfavorable conditions.
On the other hand, in such a device, when the simple electric signal relay member is constantly short-circuited, the main body of the image forming apparatus may detect that a correct developing device has been loaded, even when a developing device has not been loaded.
It is therefore an object of the present invention to provide an image forming apparatus which can solve the problem set forth above.
More particularly, an object of the present invention is to provide an image forming apparatus which can certainly prevent the loading of a developing device at an incorrect loading portion and/or prevent that developing device from being operated.
Another object of the present invention to provide an image forming apparatus which can certainly prevent a main body thereof from causing an erroneous detection that a correct developing device has been loaded, while in fact, a developing device has not been loaded, but appears to be so due to short circuiting of an electric signal relay member by something other than the developing member.
According to the one aspect of the present invention, an image forming apparatus comprises: a latent image holding body forming an electrostatic latent image; a developing device developing the electrostatic latent image to form a visible developed image using a toner, the developing device being detachably loaded in the image forming apparatus; a transfer device transferring a developed image onto a printing medium; a fixing device for fixing the transferred image; means for preventing an incorrect developing device which has been loaded in the image forming apparatus from being placed in a development enabled condition; and means for detecting the operating state of the preventing means.
According to another aspect of the present invention, an image forming apparatus comprises: a latent image holding body forming an electrostatic latent image; a developing device developing the electrostatic latent image to form a visible developed image using a toner, the developing device being detachably loaded in the image forming apparatus; a transfer device transferring the developed image onto a printing medium; a fixing device for fixing the transferred image; a main body of the image forming apparatus incorporating at least the latent image holding body; an engaging member, mounted on one of the main body of the image forming apparatus and the developing device, identifying the kind of developing device; an engagement receptacle member mounted on the other of the main body and the image forming apparatus, the engagement receptacle member being engageable with the engaging member when the developing device loaded in the image forming apparatus is other than a predetermined kind of developing device; and an electrical signal relaying member to be opened and closed by the engaging member during operation of the developing device.
In a case where the image forming apparatus is supplied as an original-equipment manufacturer (OEM) product to be sold under various commercial brands, and the developing devices and other consumable supplies are supplied exclusively for a corresponding commercial brand of image forming apparatus, it is preferred that the preventing means be capable of operation only upon loading of the developing device of correct manufacture or correctly corresponding commercial brand.
In the preferred construction, the image forming apparatus may further comprise a detecting device for detecting the presence or absence of the developing device in a redundant manner for restricting the operation of the image forming apparatus under a non-loaded condition of the developing device. The detecting means may be provided in a loading portion of the developing device in a main body of the image forming apparatus and designed to be electrically opened and closed only upon operation of the developing member. When the image forming apparatus is loaded with a plurality of developing devices, the detecting means detects the variation of one electrical signal as an output of a plurality of detecting means connected in parallel.
Also, when the image forming apparatus employs a plurality of developing devices storing a plurality of toners mutually distinct colors, the preventing means may prevent loading of the developing device of a color other than a predetermined correct color.
Preferably, the image forming apparatus is designed so that the arrangement for ensuring loading of a correct developing device as set forth above, may not be easily overridden. Thus, operation of the image forming apparatus under a condition where the developing device is not loaded can be certainly prevented.